The present invention relates to a method according to the preamble of the appended claim 1, a communication system according to the preamble of the appended claim 10, and a network element according to the preamble of the appended claim 24.
The term “wireless communication system” generally refers to any communication system which makes a wireless data transmission connection possible between a mobile station (MS) and stationary parts of the system when the user of the mobile station is moving within the operating range of the system. A typical wireless communication system is a public land mobile network PLMN. A major part of wireless communication systems at the time of filing of this application belong to so-called second-generation mobile communication systems, of which one example to be mentioned is the widely known Global System for Mobile telecommunications (GSM). The present invention is particularly well suitable for packet switched mobile communication systems under development. In this description, the General Packet Radio Service (GPRS) system will be used as an example of such a mobile communication system whose standardization is presently under way. It is obvious that the invention can also be applied in other mobile communication systems applying packet switched communication.
The general packet radio service GPRS is a new service under development in the GSM mobile communication system. The operational environment of the GPRS system comprises one or several subnetwork service areas which are combined to a GPRS backbone network. The subnetwork comprises several support nodes (SN), such as serving GPRS support nodes (SGSN). Further, the packet network comprises a packet control unit PCU which is connected to the mobile communication network (typically via a connection unit to a base transceiver station) in such a way that it can offer packet switching services to mobile stations via base transceiver stations (cells). In practical systems, a packet control unit is preferably located in a base transceiver station, in a base station controller, or in a serving support node. The mobile communication network offers the transmission of packet-switched information between the support node and the mobile station. The different subnetworks are, in turn, connected via GPRS gateway support nodes (GGSN) to an external data network, such as a public switched data network (PSDN). Thus, the GPRS services facilitates the transmission of packet-format information between the mobile station and the external data network, wherein certain parts of the mobile communication network constitute an access network.
To use GPRS services, the mobile station first performs logging in the network (GPRS attach), whereby the mobile station reports that it is ready for packet data transmission. The login makes a logical link between the mobile station and the support node SGSN, facilitating the transmission of short message services (SMS) via the GPRS network, paging services via the support node, and informing about incoming packet data to the mobile station. In connection with login of the mobile station, the support node also performs mobility management (MM) and user identification. To transmit and receive data, a packet data protocol (PDP) is activated, whereby the mobile station is allocated a packet data address to be used in the packet data connection, wherein the address of the mobile station is known in a gateway support node. Consequently, in the login, a data transmission connection is set up to the mobile station, to the support node and to the gateway support node, the connection being allocated a protocol (for example X.25 or IP), a connection address (e.g. X.121 address), quality of service, and a network service access point identifier (NSAPI). The mobile station activates the packet data connection by an activate PDP context request, in which the mobile station gives the temporary logical link identity (TLLI), the packet data connection type, the address, the required quality of service, the network service access point identifier, and possibly also an access point name (APN).
The quality of service determines e.g. the way in which packets (packet data units, PDU) are processed during the transmission in the GPRS network. For example, quality of service levels determined for connection addresses are used to control the order of transmission, buffering (packet strings) and rejection of packets in the support node and in the gateway support node particularly in situations in which there are packets to be transmitted in two or more connections simultaneously. Different quality of service classes determine different delays for the transfer of packets between different ends of the connection, different bit rates, and the number of packets to be rejected can be different in connections with different quality of service. In the GPRS system, four quality of service classes are formed to define the quality of service offered by the LLC layer for a connection.
Reliability determines if acknowledgement (ARQ) is or is not (no ARQ) used in the logical link control layer LLC and in the radio link layer RLC in the communication. Furthermore, reliability is used to define whether protected mode is used in unacknowledged data transmission and whether the GPRS backbone network applies the TCP or UDP protocol in the transmission of packets belonging to the connection.
The appended FIG. 1 shows the operation of a known LLC protocol layer 101 in a mobile station and in a GPRS support node. Block 102 shows the operations of a known RLC/MAC (radio link control/media access control) layer which are needed between the LLC layer 101 and the mobile station (not shown in FIG. 1). In a corresponding manner, block 103 shows functions of a known BSSGP (base station subsystem GPRS part) layer which are needed between the LLC layer 101 and the packet control unit PCU (not shown in FIG. 1). The interface between the LLC layer 101 and the RLC/MAC layers is called RR interface, and the interface between the LLC layer 101 and the BSSGP layers is called BSSGP interface.
Above the LLC layer 101, there are known GPRS mobility management functions 104, SNDCP functions 105 and short message service functions 106 which belong to layer 3 in this presented layer structure. Each of these blocks have one or several connections to the LLC layer 101 for coupling to its different parts. The logical link management block 107 has an LLGMM control connection (Logical Link—GPRS Mobility Management) to the block 104. Mobility management data is routed via the LLGMM connection between the blocks 104 and the first LLE (logical link entity) block of the LLC layer. The second 109, third 110, fourth 111 and fifth 112 LLE blocks are coupled to the block 105 via respective connections. These blocks are also called QoS 1, QoS 2, QoS 3 and QoS 4 according to the quality of service of the packets processed by these blocks. The sixth LLE block 113 of the LLC layer is coupled to the block 106 via an LLSMS (Logical Link—Short Message Service) connection. The service access point identifiers of the first 108, second 109, third 110, fourth 111, fifth 112, and sixth LLE blocks are 1, 3, 5, 9, 11, and 7, respectively. Each of these LLE blocks is connected in the LLC layer to a multiplexing block 114 which processes connections via the RR interface to the block 102 and further to the mobile station, as also connections via the BSSGP connection and the BSSGP block 103 to the radio system. The BSSGP block 103 is needed for the transmission of messages between the serving support node SGSN and the radio system.
The connection between the multiplexing block 114 and the block 102 of the lower layer in the direction of the mobile station is called a transmission pipe. All packet flows between the upper parts of the LLC layer and the lower layers 102 pass through the same multiplexing block 114 and the transmission pipe. For packet data transmission of the LLC layer 101, it is possible in the GPRS system to set up temporary block flows (TBF) between the mobile station and the mobile communication network. Setting up of such a temporary block flow can be started by either the mobile station or the mobile communication network. These temporary block flows are temporary block flows of the RLC/MAC layer in which information of the LLC layer is transmitted. The temporary block flow can be intended for data transmission either from the mobile communication network to the mobile station, of which the abbreviation DL TBF (downlink TBF) is used in the signalling charts of FIGS. 2, 3a and 3b and which is also called downlink in this description, or from the mobile station to the mobile communication network, wherein the abbreviation UL TBF (uplink TBF) is used respectively and which is also called uplink in this description.
FIG. 2 shows, in a signalling chart, temporary block flows applying packet data transmission according to prior art. If the mobile station has, in idle mode, packets to be transmitted, the mobile station cannot directly start the transmission of these packets, but the mobile station must first be switched from the idle mode to the active mode (packet transmission mode). After this, the mobile station starts the measures for setting up a temporary packet connection on a control channel, such as PCCCH or CCCH control channel (block 201). The transfer 205 of packets from the mobile station to the mobile communication network can be started after a temporary block flow has been set up. The signalling to be formed in the set-up is represented by arrows 202 and 203, and packet channel configuration by block 204. In connection with uplink packets, the GPRS system applies a countdown value CV whereby the mobile station MS can inform the mobile communication network when the uplink transmission is ending. Thus, the mobile station MS sets, in the last packet to be transmitted (arrow 206), information about ending of uplink packets, e.g. the final bit in the packet countdown value in the packet header to the value zero. Thus, the mobile communication network NW knows that this was the last packet to be received in this packet flow. After the transmission of the packets, and if RLC acknowledged mode was used in the packet flow, the mobile communication network transmits an acknowledgement message Packet Uplink Ack/Nack (arrow 207), in which the final bit (Final Ack Indicator, FAI) is set to the value true, preferably logical 1 state. This final bit value indicates to the mobile station that no (more) packet retransmissions are needed, but all the packets have been received. After this, the packet flow is unpacked.
When the mobile communication network receives a packet of the LLC layer addressed to the mobile station, the mobile communication network must form a temporary block flow from the base station to the mobile station for the transmission of the packet, if there is not already an existing temporary block flow. The block flow is preferably set up by means of a control channel, such as PCCCH or CCCH, by configuring a packet data traffic channel PDTCH. This is illustrated by block 208 in FIG. 2. After the packet of the LLC layer has been received in the packet control unit, the international mobile subscriber identity (IMSI) and possible parameters related to discontinuous reception (DRX) are used to find out in which time slot of the control channel it is possible to perform configuration, preferably the transmission of a channel allocation message (Packet Downlink Assignment). The calculation of this moment of time can be implemented in the packet control unit PDU, in the base station BTS or in another part of the mobile communication network. After the temporary block flow has been set up, the transmission of packets is started (arrow 209). For receiving packets, the mobile station switches over to a packet transfer mode and starts to listen to the packet data channel and to receive packets. Each RLC packet transmitted by the mobile communication network to the mobile station contains a final block indicator (FBI). The purpose of this final block indicator is to inform the mobile station when the mobile communication network has no more information to be transmitted in the block flow to the mobile station, wherein this temporary block flow can be terminated.
The mobile communication network sets information on this in the last packet to be transmitted (arrow 210), e.g. the final bit of the packets to the value true (e.g. logical 1 state). In this way, the mobile station will know that this was the last packet to be received in this block flow. This packet also contains a relative reserved block period (RRBP) in which the mobile communication network can inform the mobile station in which time slot the mobile station can transmit an acknowledgement message. After receiving this last packet, the mobile station transmits an acknowledgement message (211) to the mobile communication network in the allocated time slot and starts a timer (block 212), such as T3192 in the GPRS system, for time control. If RLC acknowledged mode was used in the block flow, the mobile station transmits a Packet Downlink Ack/Nack message in which the Final Ack Indicator (FAI) is set to the value true, preferably logical 1 state. This final ack indicator informs to the mobile communication network that no (more) retransmissions of packets are needed, but all the packets have been received. If RLC Unacknowledged Mode was used in the block flow, the mobile station transmits a Packet Control Ack message. The mobile station continues to listen to the packet data traffic channel PDTCH in case the mobile station should retransmit the acknowledgement message, until the time set in the timer T3192 has expired. After this, the mobile station preferably switches over to the idle mode.
A timer is also started in the mobile communication network, e.g. T3193 in the GPRS system, after the mobile communication network has received said acknowledgement message from the mobile station. After the time set in the timer has expired, the mobile communication network deallocates the temporary block flow.
A problem in this arrangement is, for example, that the mobile communication network may have to wait for the transmission of the channel allocation message. This may be, for example, due to the fact that the mobile communication network has set the mobile station in the mode of discontinuous reception, wherein the mobile station only listens to the control channel at certain times. The purpose of this arrangement is to reduce the power consumption of the mobile station. At the base station, there may also be several messages in a string to be transmitted in the same time slot of the control channel. Thus, depending on the parameters related to discontinuous reception as well as the loading of the base station at the moment, there can be a delay of several seconds, even about 15 seconds, in the transmission of the channel allocation message in a mobile communication network according to e.g. the GPRS system. This causes a considerably long delay in the data transmission. Furthermore, this delay can cause problems in the data transmission. For example, an application from which the packets are transmitted or in which packets are received, may conclude from the long delay that the connection to the other party is no longer in order. Thus, the application may terminate the data transmission. Such a situation may occur for example when an application being run in the mobile station has transmitted, via the mobile communication network to the other party, e.g. a server connected in the Internet data network, information, an inquiry etc., to which the application expects to receive a reply. If there are no existing temporary data transmission flows between the mobile station and the mobile communication network, a temporary data transmission flow is first set up from the mobile station to the communication network. After the transmission of the message, the data transmission flow is deblocked. At the stage when the reply comes to the mobile communication network and further to the packet control unit, a temporary data transmission flow must be set up in the above-described manner, which may thus cause such a long delay in the reception of a reply message to the application that the application has already concluded that the connection was disconnected.